Optical testing or measuring apparatus



May 30, 1944. REASON 2,349,989

OPTICAL TESTING OF. MEASURING APPARATUS Original Filed June 1, 1958 4Sheets-Sheet l /0 V80 [or Attorney May 30, 1944.

R. E. REASON 2,349,989

OPTICAL TESTING OR MEASURING APPARATUS Original Filed June 1, 1938 4Sheets-Sheet 2 May 30, 1944. R, E. REASON OPTICAL TESTING OR MEASURINGAPPARATUS Original Fild June 1, 1938 4 Sheets-Sheet 3 F ig. 9.

Fig. 10.

R. E. REASON OPTICAL TESTING OR MEASURING APPARATUS May 30, 1944.

Original Filed June 1, 1958 4 Sheets-Sheet 4 MAM 4A 6 wM/ M H mm AAttorney Patented May 30, 1944 OPTICAL TESTING B MEASURING APPARATUSRichard Edmund Reason, Leicester, England, as-

slgnor to Kapella Limited, Leicester. England, a oompany'o! GreatBritain Original application Jane 1, 1938, Serial No. Divided and thisapplication July 12,

1940, Serial No. 345,019. In Great Britain June 13 Claims. (c1. ss-wThis application is divisional from United States of America applicationSerial No. 211,231 filed June 1, 1938, Patent No. 2,258,102, September16, 1941. ihe invention relates to optical apparatus for measuring ortesting the accuracy of section profiles, especially plane sectionproflles, of manufactured articles or of appliances used in theirmanufacture, as for example for effecting precision measurements ofscrewthreads or hobs or thread gauges.

The primary object of the invention is to provide an improved opticalapparatus for effecting such precision measurement or testing, whichwill be of more general applicability than the shadow projectionarrangements hitherto known for screwthread testingand will eflect thedesired measurement with av very high degree of. accuracy.

A more precise object is to provide apparatus for measuring or testingsection profiles oi hollow or deeply reentrant objects, such for exampleasinternal screwthreads or nuts, to which the known shadow projectionarrangements are inapplicable.

These objects may be fulfilled by the use of apparatus comprising anilluminating device ,by means of which a beam of light bounded (as leaston one side) by a sharply defined surface is directed on to the surfaceof the object under examination, and an optical projecting de- 0 vice bymeans of which the diffused light from the surface of the object isutilised for the projectionof animageofthe profile in which the objectis cut by such bounding surface.

A- further object of r the invention is to provide an, improvedilluminating device for defining the section profile onthe surface ofthe object with greater accuracy than hitherto.

Still further objects of the invention will be apparent from theappended claims and from the following description of the accompanyingdrawings. which show some convenient practical alternative arrangementsaccording to the invention. In these drawings Figure 1 shows one simpleform of illuminat ingdevice more especially intended for defining thesection profile on a portion of a screwthread,

Figure 2 is a partial view of the arrangement of Figure 1 at rightangles thereto,

Figures 3 and 4 are similar views showing a preferred modification ofthe arrangement of. Figures 1 and 2,

Figures 5 and 6 illustrate a simple arran 8ement embodying theilluminating device ofFiS- Y was 3 and 4 for examining internalserewthreadl.

Figures '1 and 8 show a modification of the arrangement of Figures 5 and6,

Figures 9 to 14 illustrate a preferred arrangement, also embodying theilluminating deviceof Figures 3 and 4, for examining internalscrewthreads.

Fig. 9 is a plan view of such preferred ap paratus partly in section andwith certain parts omitted, a

Fig. 10 is a side elevation partly in section'taken from below in Fig.9,

Fig. 11 is a side elevation partly in section looking from the left inFig- 9.

Fig. 12 is a partial plan view on a larger scale showing certain partsomitted from Figs. 9 and 11,

Fig. 13 is a side elevation of parts shown. in

'Fig. 12 partly in section on the line 13-43 of Fig. '14 and showing,also, the nut to be ex,-

amined, which is indicated by dotted lines in Fig. 12, r

Fig. 14 is a view in elevation looking from the.

right in Fig. 13,

Fig. 140. is a front view of the nut carrier, Figure 15 shows amodification of the arrangement of Figures 9 to 14,

Figures 16 and 17 respectively illustrate two' alternative illuminatingarrangements especially intended for testing the pitch of ascrewthread,.

and

Figure 18 shows a modification of the arrangement of Figure 17.

The alternative illuminating devices shown in Figures 1 to 4, as alsothose of Figures 16 to 18,

are intended more especially foruse in conjunc tion with a suitablevoptical projecting device for projecting an image of the sectionprofile for precision measurement of objects such as screwthreads orgear teeth, wherein it' is necessary to take into account theshape ofthe surface of the object and to define the section profile sharply bymeans of an illuminating device suited to such shape. A suitable form ofprojecting device for use with the illuminating device will he describedlater with reference to Figures '5 to 15.

The arrangement of Figures 1 and 2 is espe-,

cially intended for illuminating a number. of noncollinear parts of theprofile, such for example as a. series of teeth of a thread A. This ar-=rangement employs a knife edge B shaped approximately to suit the shapeof the profile and an image of the knife edge is focussed by a.

single optical system on the surface of theobj'ect A, the knife edgebeing illuminated by a source of light B of small size associated with acondenser B, with or without a concave reflector behind the lightsource, so that a large .percentage of the light is collected andconcen- United States of America patent application Berial No. 279,253,which like the present application is divisional from application'serialNo.

211,231.' Thus the optical system comprises a projecting lens 28(consisting for example of a divergent component between two convergentcomponents with the modal points in the air gaps between the components)and two collimating lenses BB spaced apart symmetrically one on eitherside of the central lens 8. The two collimating lenses B B, each ofwhich may consist of an achromatized doublet, are of equal focal lengthand have their principal focal points coincident with the nodal pointsof the centrallens B The whole system is symmetrical and produces aninverted image at unit magnification, each elementary portion of theknife edge B and the corresponding elementary portion of the imagethereof being equallyinclined to the optical axis of the system.

In. the arrangement of Figures 1 and 2 the knife edge B is made bybending sheet metal to the required shape and cutting it off in a plane.It will be appreciated, however, that the knife edge may be made inother ways, as for example by milling from the solid. Figures 3 and 4illustrate such a modification, wherein a knife edge is obtained bycutting a solid counterpart escapes and serves to reflect both the beamfrom the illuminating device (which is shown as of the kind describedwith reference to Figures 3 and 4, the same reference letters beingemployed) and the beam to the projecting device, the latter beamextending obliquely to the plane of the section profile.

The oblique projecting device may be such as to give an accuratelyfocussed but distorted image of the profile, but it will usually bepreferable to employ a device giving a rectified im-, age free fromdistortion due to the oblique projection. In cases where the directionof projectlon does not make too large an angle with the perpendicular tothe plane of the section profile, saw or less, it ispossible to obtainfairly good results by using a simple wide angle lens D for projection,as shown in Figure 5, the optical axis of the lens being perpendicularto the section plane (or rather the reflection of the section plane inthe mirror C) and also to B which will mate with the object, for examplea. nut, if the object is a screwthread, in the appropriate plane andpolishing the cut surface. This polished surface acts as a reflector toreplace the portion of the cone of light which is cut off by the solidbody of the cut counterpart B and whose loss would tend to cause theformation of an unsatisfactory image of the knife edge on the surface ofthe object.

It will be noted that, with either form of knife edge, a sharply definedshadow thereof will be cast on the surface of the object, the edge ofthe shadow constituting the section profile. The diffused light from thesurface of the object is used for projecting an image of the sectionprofile, and although it would be preferable to project the image in adirection at right angles tothe plane of the profile, this will seldombe practicable, and the projecting device is there-' fore such as toproject obliquely an accurately focussed image of the profile.

When the object to be examined is hollow or deeply reentrant, as in thecase for example of a nut or internal screwthread, it is difiicult' 'No.279,253 referred to above. .jecting device comprises a projecting lens Dthe image plane, the optical axis however lying to one side of theprofil so that the rays pass beams.

. A preferred arrangement for examining internal screwthreads isillustrated in Figures 9 to 14. In this arrangement the illuminating andprojecting devices are respectively carried in tubular structures EFsupported horizontally at right angles to one another in clamps GG' on abase G which also carries a worktable G The illuminating device is shownas similar to that of Figures 3 and 4, the same reference let,- tersbeing employed and the projecting device is of the kind described in theapplication Serial Thus the prodisposed centrally between twocollimating lenses D D- the arrangement being similar to that of theoptical system used in the illuminating v device. The tubular structureF containing the projecting device is provided with an inclined supportF for a projection screen or photographic plate.

Detachably mounted at the end of the projector casing F'is a prismcarrier H containing a pair of prisms H 11 of appropriate shapes.

Fitting closely around the small end of the prism carrier H is a nutcarrier H-' which is secured by .screws H to a casing H" mounted at theend of projector casing F. Carrier 1-! has a pair of guide rails orsupports HH, which are preferably threaded as shown and may for part oftheir length be joined together to form a single wide rail or support.The nut A to be examined 1 is suspended on the guide rails, so that thepart of the nut between'the rails is at the proper position relativelyto the prisms H ll. The threading of the rails facilitates positioningof the nut longitudinally in the desired position for examination. Thisarrangement can be satisfactorily used for examining nuts of varioussizes. but if the rails are threaded, it will be necessary to employ adifferent nut carrierfor each different thread pitch. The passage of theilluminating and projecting beams through the prisms H H will be clearfrom the drawings, and it will be noticed that the arrangement issuitable for use with internal threads of small diameter relatively totheir depth. For clearness oi showing of the prism carrier H. and itscontained prisms, the nut carrier H and nut A and casing' H" are omittedfrom Figs. 9 and 11, except for a part of casing H shown in section inFig. 9,

Figure illustrates a variant of this arrangement wherein the edge 1-! ofthe casing H is formed as a knife edge for use with a collimated beam oflight obtained by illuminating a small aperture in a mask J (by means ofa source J and condenser J) at the focus of an objective J. A beam ofparallel light is thus transmitted towards the object and since theknife edge is disposed close to the surface of the internal screwthread,a sharply defined shadow is cast thereon to determine the sectionprofile.

Forthe measurement or testing of the pitch of a screwthread, two or-moreturns of the thread may be projected and their axial separation measuredon the projected image. It will usually be more accurate; however, toemploy what may be termed a "null method of measurement, by firstprojecting an image of one tooth and then moving the thread through anaxial distance equal to the pitch (or a multiple thereof) until theimage of another tooth accurately occupies the same position as thefirst image. When a photographic plate is used, the plate can bemaintained in position during movement of the thread through the correctpitch distance and reexposed so that the two images are superimposed onthe plate, the accuracy of such super-position being a test of theaccuracy of the pitch of the thread. It will usually be moresatisfactory in this case to reverse the second image, so that the pitchaccuracy can be tested in accordance with the accuracy of meshing of thetwo images. Such image reversal can obviously be obtained by rotatingthe illuminating device through 180 about its own axis between the twoexposures of the plate, so that the body of the knife edge is first onone side and then on the other side of the plane defined by the edge.The same effect can however be obtained without the necessity forrotating the whole illuminating device, and Figures 16 to 18 show somealternative arrangements of illuminating device which may beemployed'for this purpose.

In the arrangement of Figure 16 a double illuminating device is usedcomprising two sources of light KKi, each with a condenser K or K and aknife edge K or K shaped to suit the profile of the thread, a singleoptical system K bein used to focus one or the other of the two knifeedges on the surface of the object in a manner analogous to thatdescribed with reference to Figures 1 to 4. A semi-transparentreflecting surface K" is provided to enable either knife edge to beimaged by the optical system, and the selection of the knife edge to beused is effected by means of a rotatable shutter K The arrangement issuch that with the shutter in one end position the knife edge K isoperative and one side of the section plane is illuminated, whilst withthe shutter in its other end position the the section plane isilluminated.

In the arrangement of Figure 17 a single source of light L with itscondenser L is used in conknife edge K is operative and the other sideof i junction with two opposed knife edges UH shaped to suit the threadprofile, an optical system L being used to focus the knife edges on thesurface of the object. A sliding double wedge L of appropriate wedgeangle is interposed between the optical system and the knife edges, andthe arrangement is such that when one half of the wedge is operative oneknife edge determines the section plane, the light between the knifeedges illuminating one side of such plane, whilst movement of the wedgegives a displacement equal to the width of the band of light and thusbrings the other knife edge image into the section plane with consequentillumination of the" wedge may be replaced, as indicated in Figure 18,

by a tilting block L, or by any other form of deviator.

It will be appreciated that, although the foregoing arrangements havebeen described with reference'to the examination of internalscrewthreads, for which theyare more especially intended, they canreadily be applied to a variety of other uses.

What I claim as my invention and desire to secure by Letters Patent is:

1. Irroptical measuring or testing apparatus for examining plane sectionprofiles of objects having non-planar surfaces, the combination of anilluminating device for defining the profile of a plane section of theobject under examination such device comprising a plane knife edgeshaped to correspond closely to the non-linear shape of the sectionprofile and an'optical system for focussing an image of the knife edgeon the surface of the object, and means whereby the diffused light fromthe surface of the object is utilized for the optical projection of animage of the section profile, the optical system being so arranged as toproduce a rectified image free from distortion due to the obliquity ofparts of the knife edge to the optical axis of the system.

2. In optical measuring or testing apparatus for examining plane sectionprofiles of objects having non-planar surfaces, the combination of anilluminating device for defining on the surface of the object underexamination the profile of a plane section thereof, such devicecomprising a knife edge constituted by the edge of a plane section of asolid counterpart which will mate with the object and an optical systemfor focussing an image of the knife edge on the surface of the object,and means whereby the diffused light from the surface of the object isutilized for the optical projection of an image of the section profile,the optical system being so arranged as to produce a rectified imagefree from distortion due to the obliquity of parts of the knife edge tothe optical axis of the system.

3. Optical measuring or testing apparatus as claimed in claim 2, inwhich the section surface of the solid counterpart is polished so as ineffect to replace by reflection. the portion of the light out off by thebody of the counterpart.

4. In optical measuring or testing apparatus for examining plane sectionprofiles of objects having non-planar surfaces, the combination of anilluminating device for defining on the surface of the object underexamination the profile of a plane section thereof, such devicecomprising a plane knife edge shaped to correspond closely to thenon-linear shape of the profile and an optical system for focussing animage of the knife edge on the surface of the object, and an opticalprojecting device for viewing th profile obliquely to the section planeand projecting an accurately focussed image thereof, the optical systemof the illuminating device and the optical projecting device each beingso arranged as to produce a rectified image free from distortion evenwhen parts of the profile are oblique to the optical axis.

5. Optical measuring or testing apparatus for examining plane sectionprofiles of objects having non-planar surfaces, comprising an illuminating device for directing on to the ,surfacepf the object underexamination a beam of light bounded on one side by a plane, such deviceincluding at least one knife edge shaped to correspond tothe non-linearshape of the profile of the section inlwhich the object is cut by suchbounding plane and an optical system for focussing on the surface of theobject a rectified image of the knife edge free from distortion due tothe obliquity of parts of the knife edge, an-

optical projecting device for viewing the section profile in a directionoblique to the bounding plane and projecting a rectified image thereoffree from distortion due to the oblique projection, and means associatedwith the illuminating device for transferring the beam of light from oneside of the bounding plane to the other.

6. Optical apparatus as claimed in claim 5, in which the knife edge isconstituted by the edge of a plane section of a solid counterpart whichwill mate with the object, the section surface of such counterpart beingpolished so as in effect to replace by reflection the portion of thelight out off by the body of the counterpart.

7. Optical measuring or testing apparatus as claimed in claim 1, inwhich the optical system comprises a projecting lens symmetricallydisposed between two collimating lenses, and is ar ranged to give unitmagnification and to collimate the principal rays in its object andimage spaces.

8. Optical measuring or testing apparatus as claimed in claim 4, inwhich the optical systems of the illuminating device and the opticalprojecting device each comprise a system of-lenses giving unitmagnification and arranged to collimate the principal rays in the objectand image spaces.

9. Optical measuring or testing apparatus, comprising an illuminatingdevice for directing on to the surface of the object under examina-.

tion a beam of light bounded on one side by a plane, such deviceincluding two knife edges along which light is caused to pass, and apartially transparent reflector so disposed that the image of one knifeedge coincides with but is oppositely directed to the other knife edge,an optical projecting device for utilizing the diffused light from thesurface of the object to project an image of the profile of the sectionin which the object is cut by the bounding plane of the illuminatingbeam, and a movable shutter for selecting either knife edge for usewhereby by movement of the shutter the beam of light is transferred fromone side to the other of the bounding plane.

10. Optical measuring or testing apparatus for examing plane sectionprofilesof objects having non-planar surfaces, comprising anilluminating device for directing on to the surface of the object a beamof light bounded on one side by a plane and thereby defining the sectionprofile thereon, such device including two knife edges along which lightis caused to pass each shaped to correspond closely to the non-linearshape of the section profile, a partially transparent reflector sodisposed that the image therein of one knife edge coincides with but isoppositely disposed to the other knife edge, and an optical system forfocussing on to the surface of the object a rectified image of eitherknife edge free from distortion due to the obliquity of parts of theknife edge to the optical axis of the system, a movable shutter forselecting either knife edge for use whereby by movement of the shutterthe illuminating beam is transferred from one side to the other of theboundingplane, and an optical projecting device for projecting in adirection oblique to the plane of the section profile an accuratelyfocussed and rectified image of the profile free from distortion due tothe oblique projection.

11. Optical measuring or testing apparatus, comprising an illuminatingdevice for directing on to the surface of the object under examination,a beam of light bounded on one side by a plane, such device includingtwo oppositely directed knife edges along which light is caused to passand a movable deviating device acting in one position to locate theimage of one knife edge in the bounding plane and in another position tolocate the image of the other knife edge in such plane whereby bymovement of the deviating device thevbeam of light is transferred fromone side to the other of the bounding plane, and an optical projectingdevice for utilizing the difiused light from the surface of the objectfor projecting an image of the profile of the section in which theobject is cut by the bounding plane.

12. Optical measuring or testing apparatus for examining plane sectionprofiles of objects having non-planar surfaces, comprising .anilluminating device for directing on to the surface of the object a beamof light bounded on one side by a plane and thereby defining the sectionprofile thereon, such device including two oppositely directed knifeedges along which light is caused to pass each shaped to correspondclosely to the non-linear shape of the section profile and an opticalsystem for focussing on to the surface of the object a rectified imageof either mife edge free from distortion due to the obliquity of partsof the knife edge to the optical axis of the system, a movable deviatingdevice acting in one position to locate the image of one knife edge inthe bounding plane and in another position to locate the image of theother knife edge in such plane whereby by movement of the deviatingdevice the beam of the light is transferred from one side to the otherof the bounding plane, and an optical projecting device for projectingin a direction oblique to the plane of the section profile an accuratelyfocussed and rectified image of the profile free from distortion due tothe oblique projection.

13. Optical apparatus for measuring or testing the accuracy of theprofile of a plane section of an internal screw thread, comprising aplane knife edge shaped to correspond closely to the shape of thesection profile, means for illuminating the knife edge, an opticalsystem for producing a rectified image of the knife edge free fromdistortion due to the obliquity of parts of the knife edge to theoptical axis of the system, a reflecting device arranged and located soas to defiect the beam from such optical system on to an internal orreentrant surface of said screw thread whereby the image of the knifeedge is formed substantially on such surface and defines the sectionprofile thereon, a further reflecting device, and an optical projectingdevice so arranged and located as to receive from such furtherreflectinl device a reflection of a beam oi! light proceeding from thesection profile in a direction oblique to the section plane and projectan accurately focussed and rectified image of the section profile freefrom distortion due to the oblique projection, and means for holding thescrew thread in a pre- I said screw thread.

RICHARD EDMUND REASON.

